1. Related Field
The present invention relates to a method and a system for navigation of an aerial vehicle. It also relates to a computer program and a computer program product for navigation of an aerial vehicle.
2. Description of Related Art
Navigation of vehicles, especially aerial vehicles, is today often based on a global navigation satellite system (GNSS), like GPS. This has the advantage that the position of the own vehicle is quite well known within some uncertainty. It can, however, happen that a vehicle has to travel through an area where a GNSS-signal is denied, for example during war or conflicts, or since some entity for whatever reason uses interfering transmitters to disturb GNSS-signals. Also technical failures might in principle cause GNSS-signal interruption.
To be able to navigate without GNSS some vehicles have inertial measurements units (IMU) on board. They can be used to keep track of the vehicle's current position using a process called dead reckoning. These IMU-systems have, however, the tendency that the calculated position will differ from the real position more and more with time. This is due to the fact that errors entering the calculations add up. Therefore, the longer the time a vehicle navigates with an IMU only, the bigger the uncertainty about the actual real position of that vehicle.
To lower the uncertainty of the actual real position and to lower the difference between a calculated actual position and the real actual position one can use an IMU with better components. This does, however, only lower the errors and the differences, whereas the total error and the total uncertainty still increase as time goes by. On the other hand, an IMU with better components usually increases the weight of the IMU substantially. Especially for airborne vehicles, this can result in the constraint that less fuel can be transported by the airborne vehicle and that, depending on the size of the airborne vehicle, therefore the range can be lowered drastically. It exists therefore a need for a navigation method in GNSS denied areas wherein the position errors do not add up with time.
EP 2 144 038 A2 discloses an inertial measurement using an imaging sensor and a digitized map. The system determines a vehicle's attitude and position based on extracting at least three features out of image data. Depending on the environment the extraction of at least three features can be different or even impossible to perform. Still GPS or similar systems are needed for determining an absolute position.